Q: A scientist uses PCR to amplify a DNA sample. After 30 cycles, approximately how many copies of the original DNA molecule will be present, assuming perfect efficiency? Use the formula $$N = N_0$ \times 2^n$$, where $$N_0 is $$the initial number of molecules and $$n is $$the number of cycles.

$$N = 1 \times 2$$^{30}$$ = 1,073,741,824$$

Question 1

Which of the following best describes the structure of a DNA molecule?

Accepted Answer

A double helix composed of two strands of nucleotides held together by hydrogen bonds between complementary bases

Question 2

What is the function of DNA in living organisms?

Accepted Answer

To serve as the instruction manual for building and maintaining an organism

Question 3

During DNA replication, which enzyme is responsible for unwinding the DNA double helix?

Accepted Answer

Helicase

Question 4

If a segment of DNA has the sequence $$5'-ATCGGTA-3'$$, what is the complementary sequence on the opposite strand?

Accepted Answer

$$3'-TAGCCAT-5'$$

Question 5

Short Tandem Repeats (STRs) are used in DNA profiling because:

Accepted Answer

They vary in length and sequence between individuals, allowing for unique identification

Question 6

Which of the following best explains why DNA evidence is considered more reliable than other forms of forensic evidence?

Accepted Answer

The probability of two unrelated individuals sharing the same DNA profile at multiple STR regions is extremely small

Question 7

What is the role of DNA polymerase during DNA replication?

Accepted Answer

It adds new nucleotides to the growing DNA strand using complementary base pairing rules

Question 8

A scientist uses PCR to amplify a DNA sample. After 30 cycles, approximately how many copies of the original DNA molecule will be present, assuming perfect efficiency? Use the formula $$N = N_0$ 	imes 2^n$$, where $$N_0 is $$the initial number of molecules and $$n is $$the number of cycles.

Accepted Answer

$$N = 1 	imes 2$$^{30}$$ = 1,073,741,824$$

Question 9

Which of the following statements about human chromosomes is correct?

Accepted Answer

Humans have 23 pairs of chromosomes, with one chromosome of each pair inherited from each parent

Question 10

Gel electrophoresis separates DNA fragments based on which property?

Accepted Answer

The length (size) of the fragments

Question 11

Why is it important to analyze multiple STR regions when creating a DNA profile?

Accepted Answer

It increases the certainty that the profile is unique to an individual

Question 12

Which of the following is NOT a component of a DNA nucleotide?

Accepted Answer

A ribose sugar

Question 13

A forensic scientist finds two DNA samples with identical STR profiles at all tested regions. What is the most likely explanation?

Accepted Answer

The samples are from identical twins or the same individual

Question 14

Which base pairs with cytosine in the DNA double helix?

Accepted Answer

Guanine

Question 15

In a DNA molecule, the backbone is formed by which components?

Accepted Answer

Alternating sugar and phosphate groups

Question 16

Which process allows scientists to make billions of copies of a specific DNA sequence in the laboratory?

Accepted Answer

Polymerase Chain Reaction (PCR)

Question 17

A cell undergoes DNA replication. If the original DNA molecule is composed of two strands, what will be the composition of the two resulting DNA molecules?

Accepted Answer

Each will have one original strand and one newly synthesized strand

Question 18

Which of the following best explains the importance of complementary base pairing in DNA replication?

Accepted Answer

It ensures that each new DNA molecule is an exact copy of the original

Question 19

A DNA sample is collected from a crime scene and analyzed for STRs. The resulting profile matches a suspect. What is the main limitation of this evidence?

Accepted Answer

It cannot distinguish between identical twins

Question 20

Which of the following is a real-world application of DNA profiling?

Accepted Answer

Identifying individuals in criminal investigations

DNA Structure and Replication: Study Notes

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